This invention relates to improved piston constructions, and more specifically, to improved means for stressing ring band inserts in pistons to preclude their loosening during operation of an engine employing such pistons.
Prior art of possible relevance includes U.S. Pat. Nos. 2,349,919 issued May 30, 1944 to Starr; and 3,321,824 issued May 30, 1967 to Porkess et al.
Many engines today, particularly those using pistons formed of light weight metals, such as aluminum, employ ring groove band inserts formed of significantly harder metals for receipt of one or more compression rings.
In some constructions, the ring groove band insert is cast in place and generally is formed of a high nickel content iron or some other hard material having a coefficient of thermal expansion approximating that of the lighter, piston body. The fabrication of such pistons requires carefully controlled casting techniques to assure good bonding of the insert to the piston body and ultrasonic inspection is generally required to check the bond. Nonetheless, there is a tendency of the insert to loosen from the piston body which can result in piston failure.
Other techniques have also been employed. For example, in the above identified Starr patent, a threaded retainer, with or without a washer is employed to hold the insert in place.
In the above identified Porkess et al patent, it is suggested that a washer be employed as a wearing surface on one side of a groove for receipt of a piston ring. However, fairly complicated rolling techniques are required to provide the desired configuration of the washer within the groove.